Remove "Installer build and test" and "Libraries Test Run" jobs once Helix Job Monitor is enabled #131615

Once Helix Job Monitor is enabled, we should remove the separate "Installer build and test" jobs as well as the "Libraries Test Run" jobs.

Those job splits exist primarily for the following reasons:

• Ensure that we don't delay other test legs from running while tests run on Helix.
• Ensure that we can easily trigger reruns of just test execution instead of redoing product build as well.
  • Matters less with Build Analysis nowadays

These concerns are significantly less impactful when sending jobs to helix doesn't block on their completion (ie we don't wait for tests to finish to build more tests).